The present invention relates to a magnetic recording medium with high surface recording density, and also to a magnetic recording mode using a large capacity floppy disk providing high reliability for practical use.
In a magnetic recording medium such as magnetic tape, hard disk, etc., a vacuum-deposited tape or a metal thin film type hard disk, etc. are used. Using a ferromagnetic metal thin film prepared by vacuum film forming method, i.e. sputtering method, vacuum evaporation method, etc., this magnetic recording medium is used as a recording layer in practical application. In this type of magnetic recording medium, high magnetic energy can be easily obtained, and flat surface can be easily achieved by smoothening the surface of non-magnetic substrate. In this respect, it is characterized in that spacing loss is low and high electromagnetic transfer characteristics can be attained, and this is suitable for a method to manufacture a high-density recording material. In particular, the sputtering method can increase magnetic energy than the evaporation method, and this is adopted in the magnetic recording medium such as hard disk, which must provide high surface recording density.
On the other hand, compared with the hard disk, a floppy disk type magnetic recording medium has higher impact resistance and can be produced at lower cost, and it is widely used in 2HD class products. Further, in recent years, a high-density magnetic recording medium represented by Zip (Iomega Inc.) based thin layer coating technique has been introduced to practical use. In the magnetic recording medium as described above, recording and reproduction are performed at high speed of about 3000 rpm, and high transfer rate closer to that of hard disk can be achieved. However, its recording density is still less than {fraction (1/20)} of that of the hard disk. This is attributable to the fact that a floppy disk type magnetic recording medium which has the magnetic layer produced by sputtering method as in case of the hard disk is not yet suitable for practical application.
There are various reasons for this. One of the reasons is that, in the magnetic recording mode using such a floppy disk, it is difficult to maintain high running durability and to attain high reliability for practical use.
In the floppy disk with the magnetic layer produced by the sputtering method, it is more difficult to maintain durability than the floppy disk produced by the conventional coating method. The reason is as follows: The floppy disk produced by the coating method contains hard particles and lubricant in the magnetic layer in addition to magnetic particles and has high lubricating property and high wear resistance. On the other hand, in the floppy disk produced by the sputtering method, the magnetic layer is a metal thin film, which is easily worn out.
For this reason, there have been attempts to form a wear-resistant protective layer on the magnetic layer as in the case of hard disk, and to form a lubricating layer on it in order to provide higher lubricating property and wear resistance. However, even when a protective layer and a lubricating layer similar to the case of the hard disk are formed on the floppy disk, running durability can be improved but it is not possible yet to attain high reliability for practical use. In case of hard disk, when the number of revolutions of disk is increased, the head is floated up by floating force applied on the head, and it is used under the condition that the head and the hard disk are not in contact with each other. In case of floppy disk, even when the number of revolutions of the disk is increased, vibration of the disk (surface deviation) is high, and the head cannot be floated up in stable manner. Even at high-speed rotation,-the head and the floppy disk are frequently in contact with each other.
For this reason, with the purpose of increasing the running durability and of maintaining high reliability for practical use in case of the floppy disk, it is necessary to achieve as follows:
(1) Lubricating layer having high lubricating property;
(2) Protective layer with high wear resistance;
(3) Well-controlled surface roughness not to generate high frictional force even when head and disk are in contact with each other; and
(4) Low surface deviation to reduce frequency of contact. In particular, for the lubricating layer and the protective layer must have higher durability in the contact sliding than those used on hard disk.
As the protective layer with high wear resistance, an amorphous carbon film containing carbon and hydrogen and called xe2x80x9cdiamond-like carbonxe2x80x9d (DLC) is most commonly used. It is used as the protective layer for hard disk or for video tape having metal thin film type magnetic layer and formed by vacuum deposition. Diamond-like carbon can be relatively easily produced. It is hard and has low frictional force and is very unlikely to cause seizure. However, it has been found that, when the commonly used diamond-like carbon containing carbon and hydrogen is used as the protective layer for floppy disk, sufficient durability cannot be obtained. The reason for this is that, when diamond-like carbon is used as a protective layer, frictional force is gradually increased as the head and the disk are repeatedly brought into contact with each other. As a result, the diamond-like carbon may be destroyed or the magnetic layer may be destroyed, and scratches may occur.
To reduce the increase of frictional force, various methods for improvement are proposed such as the improvement of structure of lubricant, adsorbing property between lubricant and protective layer, surface treatment of protective layer, property of protective layer, etc. In order to maintain low frictional force even when lubricant or protective layer is consumed or worn out, it seems to be the most effective way to decrease frictional coefficient of the protective layer itself.
For example, as a method to improve the quality of the protective layer of hard disk, there is a method to add a third element in addition to carbon and hydrogen of the diamond-like carbon. Above all, it is reported that a nitrogen-added diamond-like carbon has an effect to decrease the frictional force. For example, JP-A-7-334830, to JP-A-1-320622, etc. describe the use of a DLC film containing nitrogen as the protective layer.
Further, JP-A-6-333231 discloses the use of a protective layer containing hydrogen and nitrogen and a lubricant layer having polar group. U.S. Pat. No. 5,567,512 (JP-A-8-106629) describes a carbon protective layer having a specific ratio of surface density of nitrogen atoms.
Also, JP-A-9-288818 describes a carbon protective layer containing nitrogen and of 10-20 nm in thickness. JP-A-10-143836 discloses that nitrogen concentration in the carbon protective layer is changed in direction of thickness and a material having a specific chemical structure is used as lubricant. Further, U.S. Pat. No. 5,776,602 teaches a nitrogen-containing carbon protective layer having Raman spectrum of a specific range. EP-54720 describes the use of a carbon protective layer containing hydrogen and nitrogen and with thickness of less than 20 nm.
On the other hand, the magnetic head sliding with the floppy disk is mounted on a slider, which generally controls floating and contact conditions. Like the slider used in the hard disk drive, the slider for the floppy disk is made of ceramics such as Al2O3xe2x80x94TiC. However, carbon protective layer is not formed on the surface of the slider as in the case of the slider for hard disk drive described in JP-A-8-45045. The reason for this may be as follows: When a conventional thin film coating type floppy disk is used as a magnetic recording medium, even in case high hardness carbon protective layer is provided, this protective layer is worn out within short time due to sliding movement with the floppy disk and the effect is very low.
The surface of the slider of hard disk drive is manufactured in such manner that it is floated stably by air flow generated by the rotation of the disk. Unlike the case of the hard disk, stable floating cannot be attained in case of the floppy disk, and it is designed to maintain very slight contact sliding. Therefore, not only the wearing of the medium but also wearing of head and slider are very important in the evaluation of the reliability of the system. When the head is worn out, it is difficult to record or reproduce the information. If the slider is worn out, powder material generated by wearing enter between the head and the disk, and this may cause reading error when the recorded signal is read, or the floppy disk may be damaged.
The problems of wearing of disk and head as described above are very important to maintain high reliability for practical use in case of magnetic recording mode, which uses a large capacity floppy disk, and has higher recording density compared with the conventional type floppy disk system. In particular, when it is tried to use metal thin film type floppy disk as the floppy disk, it is very difficult to solve these problems. To solve the problems, it is attempted in the present invention to maintain high reliability for practical use in the magnetic recording mode using a floppy disk and providing high recording density using a metal thin film type floppy disk.
Also, it has been found that satisfactory durability cannot be obtained even when the commonly used DLC is used as protective layer for floppy disk. When DLC is used as the protective layer, head and disk are repeatedly brought into contact with each other, and frictional force is gradually increased. As a result, DLC film is destroyed or the magnetic layer is destroyed, and scratches occur.
To reduce the increase of frictional force, various methods for improvement are proposed such as the improvement of structure of lubricant, adsorbing property between lubricant and protective layer, surface treatment of protective layer, property of protective layer, etc. In order to maintain low frictional force even when lubricant or protective layer is consumed or worn out, it seems to be the most effective way to decrease frictional coefficient of the protective layer itself.
However, when nitrogen is added to DLC in the protective layer of floppy disk, friction coefficient is certainly decreased, but running durability is often decreased. This is because, even though friction coefficient is decreased due to the difference in manufacturing conditions and the difference in nitrogen content, hardness is decreased, and satisfactory wear resistance cannot be attained.
Generally, when nitrogen is added to DLC, frictional force is gradually decreased with the increase of the added nitrogen quantity, and hardness is gradually decreased (aggravated). Therefore, in order to maintain sufficient running durability in the severe sliding conditions such as the case of floppy disk, a protective layer must be prepared, which has such composition and structure that satisfactory hardness can coexist or is compatible with friction coefficient. To cope with such problem, it is proposed to coat relatively soft nitrogen-added DLC on a hard DLC, but this requires more complicated manufacturing procedure.
It is an object of the present invention to prepare a protective layer where high hardness and low friction coefficient can coexist and to provide a magnetic recording medium which has satisfactory running durability not only when it is used on a rigid support member such as hard disk but also when it is used under severe sliding condition as in the case of floppy disk.
The problem of wearing of disk and head is very important in case of the magnetic recording mode using a large capacity floppy disk having higher recording density than the conventional type floppy disk system. In particular, when a metal thin film type floppy disk is used as floppy disk, it is very difficult to solve this problem.
In this respect, it is another object of the present invention to provide a magnetic recording medium, which has a protective layer where high hardness and low friction coefficient can coexist and by which high running durability can be attained in case of magnetic disk such as hard disk or floppy disk.
It is aimed to maintain high reliability in practical use in a magnetic recording mode using a floppy disk and providing high recording density using a metal thin film type floppy disk.
The present invention provides a magnetic disk which comprises a magnetic layer, a protective layer, and a lubricating layer coated at least on one surface of a flexible support member, wherein the protective layer contains at least carbon, hydrogen and nitrogen.
Further, the present invention provides a magnetic disk, which comprises a magnetic layer, a protective layer, and a lubricating layer coated at least on one surface of a flexible support member or a rigid support member, wherein the protective layer contains at least carbon, hydrogen, nitrogen and rare gas elements.
Also, the present invention provides the magnetic disk as described above, wherein nitrogen content of the protective layer is 0.5-8.0 atom %.
Further, the present invention provides the magnetic disk as described above, wherein hydrogen content of the protective layer is 25-35 atom %.
Also, the present invention provides the magnetic disk as described above, wherein carbon content in the protective layer is 60-70 atom %.
Further, the present invention provides the magnetic disk as described above, wherein rare gas content in the protective layer is 0.5-1.2 atom %.
The present invention provides a method for manufacturing a magnetic disk, which comprises the steps of forming a magnetic layer at least on one surface of a flexible support member or a rigid support member, and forming a protective layer on surface of the magnetic layer by plasma CVD method using a mixed gas of hydrocarbon, nitrogen and rare gas elements under application of negative bias voltage on the magnetic layer.
Also, the present invention provides the method for manufacturing a magnetic disk as described above, wherein the magnetic layer is formed by sputtering method.
Further, the present invention provides a magnetic recording mode using a floppy disk, wherein the floppy disk is used as a magnetic recording medium, said floppy disk comprising a ferromagnetic thin film and a carbon protective layer coated at least on one surface of a flexible support member, and a magnetic signal is recorded and reproduced by a floppy disk device with a carbon protective layer provided on surface of a head or a slider.
Also, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein hardness of the carbon protective layer of the floppy disk is lower than hardness of the carbon protective layer on the surface of the head or the slider.
Further, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein micro-hardness of the carbon protective layer of the floppy disk is within the range of 20-40 GPa, micro-hardness of the carbon protective layer on the surface of the head or the slider is 30 GPa or more, and hardness of the carbon protective layer on the floppy disk is lower than hardness of the carbon protective layer on the surface of the head or the slider.
Also, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein a floppy disk is used as a magnetic recording medium, said floppy disk having a ferromagnetic metal thin film at least on one surface of a flexible support member and comprising a carbon protective layer containing at least carbon, hydrogen and nitrogen coated on a ferromagnetic metal thin film, and a magnetic signal is recorded and reproduced by a floppy disk device having a carbon protective layer on the surface of the head or the slider.
Further, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein hydrogen content in the carbon protective layer of the floppy disk is 25-35 atom %, and nitrogen content is 0.5-8.0 atom %
Also, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein the carbon protective layer of the floppy disk contains at least carbon, hydrogen, nitrogen, and rare gas elements.
Further, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein the carbon protective layer of the floppy disk contains at least carbon, hydrogen, nitrogen, and rare gas elements, hydrogen content is 25-35 atom %, nitrogen content is 0.5-8.0 atom %, and rare gas content is 0.5-1.2 atom %
Also, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein micro-hardness of the carbon protective layer of the floppy disk is within the range of 20-40 GPa, micro-hardness of the carbon protective layer on the surface of the head or the slider is 30 GPa or more, and hardness of the carbon protective layer of the floppy disk is lower than hardness of the carbon protective layer on the surface of the head or the slider.
Further, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein the floppy disk is used as a magnetic recording medium, said floppy disk comprising a ferromagnetic metal thin film at least on one surface of a flexible support member and having a carbon protective layer containing at least carbon, hydrogen and nitrogen on the ferromagnetic metal thin film, and a magnetic signal is recorded and reproduced on a floppy disk device having a carbon protective layer containing at least carbon and hydrogen on the surface of the head or the slider.
Also, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein hydrogen content in the carbon protective layer of the floppy disk is 25-35 atom %, and nitrogen content is 0.5-8.0 atom %.
Further, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein the carbon protective layer of the floppy disk contains at least carbon, hydrogen, nitrogen, and rare gas elements.
Also, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein the carbon protective layer of the floppy disk contains at least carbon, hydrogen, nitrogen, and rare gas elements, hydrogen content is 25-35 atom %, nitrogen content is 0.5-8.0 atom %, and rare gas content is 0.5-1.2 atom %.
Further, the present invention provides a magnetic recording mode using a floppy disk as described above, wherein micro-hardness of the carbon protective layer of the floppy disk is within the range of 20-40 GPa, micro-hardness of the carbon protective layer on the surface of the head or the slider is 30 GPa or more, and hardness of the carbon protective layer of the floppy disk is lower than hardness of the carbon protective layer on the surface of the head or the slider.